An inspection system for inspecting a lighting device during an assembly process of the lighting device and a method thereof

ABSTRACT

An inspection system ( 100 ) for inspecting a lighting device ( 150 ) during an assembly process of the lighting device; wherein the lighting device comprises a base plate ( 153 ) and a plurality of components ( 155 ) mounted on the base plate; wherein the inspection system comprises: a light source ( 120 ) arranged for illuminating the lighting device according to a first light output spectrum for providing a luminance contrast between the base plate and the plurality of components; an imaging unit/camera ( 130 ) arranged for capturing a first image of the illuminated lighting device; a controller ( 110 ) comprising a processing unit for determining a luminance contrast measure of the captured first image; wherein the processing unit is further arranged for, when the luminance contrast measure of the captured first image exceeds a threshold value, adapting the first light output spectrum, and wherein the imaging unit is further arranged for capturing a second image of the lighting device illuminated according to the adapted first light output spectrum; and wherein the controller further comprises: a comparing unit arranged for comparing the second image with a reference image; a determination unit arranged for determining a defect in the base plate and/or in the plurality of components based on the comparison.

FIELD OF THE INVENTION

The invention relates to an inspection system for inspecting a lightingdevice during an assembly process of the lighting device. The inventionfurther relates to a method and a computer program product forinspecting a lighting device during an assembly process of the lightingdevice.

BACKGROUND

A LED (Light Emitting Diode) is a solid semiconductor device that canconvert electric energy into visible light. The LED becomes an ideallight source that takes the place of conventional light sources due toadvantages of small volume, low power consumption, long service life,high brightness, low heat quantity, environmentally friendly,durability, and the like. LEDs are applied quite flexibly and may bemade into small thin products in various forms of points, lines, andplanes. LEDs have been widely applied to various types of lightingdevices, such as a battery-powered flashlight, a mini-sized soundcontrol lamp, a safety flare, illuminating lamps for roadways and indoorstairs, and building and marker continuous lighting lamps.

As the demand of LED (or LED-based lighting devices) is increasing, theproduction of LED (or LED-based lighting devices) is also increasing. Toautomate End-of-Line product quality control and process execution ofLED (or LED-based lighting devices) production, e.g. checking theexecution of required process steps, checking the quality of suchexecuted process steps, computer vision (or machine learning) techniquesare being applied. In such techniques, typically visual light-basedimaging technologies are used.

US 2004/184031A1 discloses a three-dimensional optical inspection systemwhich reconstructs a three-dimensional image of the shape of the surfaceof an at least partially specular object resident on a printed circuitboard by capturing two or more two-dimensional images of the objectunder different illumination configurations. The diffuse reflection, aswell as the specular reflection can be used to reconstruct thethree-dimensional image using any reconstruction method, such asphotometric stereo. The different illumination configurations can beachieved using an illumination source including light-emitting elementsarranged in concentric circular arrays, in which each of the circulararrays is divided into sections. Each section is independentlycontrolled to selectively activate the sections to illuminate the objectin a pre-established illumination pattern.

SUMMARY OF THE INVENTION

The inventors have realized that the use of computer vision techniquesin LED assembly process automation has severe limitations in recognizingdefects in LED (or in LED-based lighting devices) leading to e.g. wrongor no detection of defects. For example, it becomes very difficult whena white object feature (e.g. a white-painted electronic driver) needs tobe recognized and captured versus a white background (a white-paintedmetal carrier plate). Or as another example, to recognize aquasi-transparent lens plate on top of a printed board and analyze e.g.the alignment of lens plate versus printed board features is verydifficult.

It is therefore an object of the present invention to provide a systemwith an improved recognition of defects in (LED-based) lighting devicesduring the assembly process, e.g. for the automated tracking of theassembly process of the lighting device.

According to a first aspect, the object is achieved by an inspectionsystem for inspecting a lighting device during an assembly process ofthe lighting device; wherein the lighting device comprises a base plateand a plurality of components mounted on the base plate; wherein theinspection system comprises: a light source arranged for illuminatingthe lighting device according to a first light output spectrum forproviding a luminance contrast between the base plate and the pluralityof components; an imaging unit arranged for capturing a first image ofthe illuminated lighting device; a controller comprising a processingunit for determining a luminance contrast measure of the captured firstimage; wherein the processing unit is further arranged for, when theluminance contrast measure of the captured first image exceeds athreshold value, adapting the first light output spectrum, and whereinthe imaging unit is further arranged for capturing a second image of thelighting device illuminated according to the adapted first light outputspectrum; and wherein the controller further comprises: a comparing unitarranged for comparing the second image with a reference image; adetermination unit arranged for determining a defect in the base plateand/or in the plurality of components based on the comparison.

The inspection system comprises a light source for illuminating thelighting device according to a first light output spectrum. The lightsource may be external to the lighting device. The first light outputspectrum may comprise a first wavelength or a first wavelength range.For example, the first light output spectrum may be a blue color withwavelength between approximately 380 nm and 500 nm. The first lightoutput spectrum may be used to provide a luminance contrast between thebase plate and the plurality of components. Luminance contrast is thedifference in luminance or color that makes an object (or itsrepresentation in an image or display, e.g. a base and a plurality ofcomponents in an image), distinguishable.

The inspection system further comprises an imaging unit arranged forcapturing a first image of the illuminated lighting device. The imagingunit may be a camera. The imaging unit may be a 2D video camera, astereo video camera, a depth-aware (ranging) video camera (e.g.time-of-flight camera). An imaging unit may comprise one or more imagingdevices. The illuminated lighting device may be illuminated with thefirst light output spectrum.

The inspection system further comprises a controller comprising aprocessing unit for determining a luminance contrast measure of thecaptured first image. The Luminance contrast measure may comprise pixelsintensity of an image, e.g. the pixel intensity of the base plate andthe plurality of components of the lighting device. A pixel is aphysical point in an image, or the smallest addressable element in anall points addressable display device; so, it is the smallestcontrollable element of an image represented on a screen. For example,pixels in grayscale images may need one byte, e.g. to represent amountof gray intensity, to render the pixel on the screen. The pixels incolor images are represented by three values of Red, Green and Blue(r,g,b). The values indicate the intensity of red, green, and blue,respectively, needed to render the pixel on the screen. The luminancecontrast measure may comprise be a (abrupt) change of intensity ofpixels in an image, for instance, change of intensities of pixels of theplurality of components with respect to the base plate. Additionally,and/or alternatively the luminance contrast measure may comprise one ormore of: Weber contrast, Michelson contrast, RMS contrast etc.

The processing unit may be further arranged for, when the luminancecontrast measure of the captured first image exceeds a threshold value,adapting the first light output spectrum, thus optimizing the firstlight output spectrum. The imaging unit may be (then) further arrangedfor capturing a second image of the lighting device illuminatedaccording to the adapted first light output spectrum. The controller mayfurther comprise: a comparing unit may be arranged for comparing thesecond image with a reference image; a determination unit may bearranged for determining a defect in the base plate and/or in theplurality of components based on the comparison. Since, the inspectionsystem optimizes the light output spectrum of the light source, anddetermines defects in the base plate and/or in the plurality ofcomponents based on captured images of the lighting device according tothe optimized light output, an improved system with an improvedrecognition of defects in (LED-based) lighting devices during theassembly process is provided. The provided system is not limited toLED-based lighting devices but also provides improved recognition ofdefects for other lighting devices.

In an embodiment, the comparing unit may be arranged for, when theluminance contrast measure of the captured first image does not exceedthe threshold value, comparing the first image with the reference image.

In an example, the luminance contrast measure of the captured firstimage may already be sufficient for inspecting the base plate and/or theplurality of components. In other words, the first light output spectrummay be optimal for the base plate and/or the plurality of componentsand, hence, doesn't require to be adapted. For example, the first lightoutput spectrum may be based on expert knowledge. Therefore, in suchsituations, the anomaly detection may be based on the comparison of thefirst image with the reference image of the lighting device. Thereference image may comprise an image of the lighting device withoutdefects in the base plate and in the plurality of components.

In an embodiment, the processing unit may be arranged for obtaining asignal indicative of optical properties of the base plate and/or theplurality of components; adapting the first light output spectrum basedon obtained optical properties.

A signal indicative of optical properties of the base plate and/or theplurality of components may be obtained. The optical properties of amaterial define how it interacts with light. For each material, e.g. thebase plate and/or the plurality of components, the incident radiation ispartially transmitted, partially reflected and partially absorbed.Therefore, the optical properties may comprise transmissivity,reflectivity and absorptivity etc. The first light output spectrum maybe advantageously adapted based on these optical properties to improveluminance contrast.

In an embodiment, the processing unit may be arranged for adapting thefirst light output spectrum by sequentially increasing or decreasing thefirst light output spectrum. Additionally, or alternatively to adaptingthe first light output spectrum based on the obtained opticalproperties, the processing unit may scan all spectrum (wavelengths)sequentially and use a hit and trial method of optimizing the firstlight output spectrum. The scanning of spectrums may be performed via afeedback loop.

In an embodiment, the lighting device may be unpowered during theassembly process.

During the assembly process, the lighting device does not receiveelectrical power, e.g. it is unpowered. The plurality of components,e.g. LEDs, mounted on the base plate may be unpowered to illuminate thelighting device. Therefore, a light source which is external to thelighting device may be used to illuminate the lighting device and thefirst light output spectrum may be optimized to improve the luminancecontrast.

In an embodiment, the plurality of components may comprise at least aphosphor coated LED.

The plurality of components may comprise at least a phosphor coated LED.In other examples, the plurality of components may further compriseelectronic LED driver(s), screw drivers, wires etc. The LEDs may becoated with phosphor, e.g. to convert blue to mixed white. Although theyellow phosphor provides some contrast between the LED and the baseplate but the effect of it is low.

In an embodiment, the first light output spectrum may be a blue lightspectrum or a UV light spectrum.

In an example, the first light output spectrum may be a light spectrumthat causes the plurality of components to emit light which isdetectable for the imaging unit. For example, for phosphor coated LEDusing a blue light spectrum may provide a detectable image with improvedluminance contrast for the anomaly detection. In an other example, UVspectrum may be used to improve luminance contrast for fluorescentcomponents of the plurality of components such as labels, paints andglue material.

In an embodiment, the comparing unit may be arranged for using computervision and/or machine learning algorithms for image comparison.

Different state-of-the-art computer vision and/or machine learningalgorithms may be used for image comparison. For example, Generativeadversarial networks GANs may be used as a machine learning algorithm todetermine anomaly (defect) in the base plate and/or the plurality ofcomponents.

In an embodiment, the threshold value may be determined by the computervision and/or the machine learning algorithms.

In this advantageous embodiment, the threshold value for the luminancecontrast measure may be determined by the computer vision and/or themachine learning algorithms. For example, the threshold value may bedetermined when a certain accuracy level of the computer vision and/ormachine learning algorithms is achieved. Alternatively, the thresholdvalue may be selected by a user.

In an embodiment, the light source may be a multispectral light sourcearranged for illuminating the lighting device at least according to thefirst light output spectrum and a second light spectrum; wherein theprocessing unit may be further arranged for, when a luminance contrastmeasure of an image of the lighting device illuminated by themultispectral light source exceeds a threshold value; adapting the firstlight output spectrum and/or the second light spectrum.

In an example, the light source may be a multispectral light source. Amultispectral light source is a light source capable of emitting morethan one spectral light content. In an alternate example, the lightsource may comprise a plurality of light sources arranged for emittingmultiple spectrums. In an example, the first light output spectrum mayprovide a background illumination to make the overall plurality ofcomponents visible, and the second light output spectrum may provide anincreased luminance contrast for one or more of the plurality ofcomponents which are not distinguishable with the first light outputspectrum. In an example, the first light output spectrum may be a whitelight and the second light output spectrum may be a UV light spectrum,e.g. to enhance phosphorescence. In another example, the multispectrallight source may be arranged for using polarized light.

In an embodiment, the imaging unit may be a multi-spectral sensingdevice.

A multispectral image is one that captures image data within specificwavelength ranges across the electromagnetic spectrum. A multi-spectralsensing device may be advantageously used to capture a multispectralimage of the lighting device.

In an embodiment, wherein the imaging unit may comprise a thermalimaging device arranged for capturing a first thermal image of theilluminated lighting device illuminated according to the first lightoutput spectrum and/or a second thermal image of the illuminatedlighting device illuminated according to the adapted first light outputspectrum.

In an embodiment, wherein the comparing unit may be further arranged forcomparing the first or the second thermal image with a reference thermalimage; and the determination unit may be further arranged fordetermining a defect in the base plate and/or in the plurality ofcomponents based on the comparison.

The light actuation on the lighting device may result in an increasedtemperature of at least a plurality of components, e.g. parts thatcontains phosphor, based on the Stokes shift of that phosphor during theconversion of light. The imaging unit may comprise thermal visiondevice, e.g. a thermal camera, to capture a first and/or a secondthermal image of the lighting device. The first thermal image of thelighting device may be captured when the lighting device is illuminatedaccording to the first light output spectrum and the second thermalimage may be captured when the lighting device is illuminated accordingto the adapted first light output spectrum. These thermal images may becompared with a reference thermal image, wherein the reference thermalimage may represent a correct (without defects) thermal distribution ofthe base plate and/or of the plurality of components, for determiningdefects in the base plate and/or the plurality of components. This willprovide a further improved determination of defects in the lightingdevice.

According to a second aspect, the object is achieved by a method forinspecting a lighting device during an assembly process of the lightingdevice; wherein the lighting device comprises a base plate and aplurality of components mounted on the base plate; wherein the methodcomprises the steps of: illuminating the lighting device according to afirst light output spectrum for providing a luminance contrast betweenthe base plate and the plurality of components; capturing a first imageof the illuminated lighting device; determining a luminance contrastmeasure of the captured first image; and wherein when the luminancecontrast measure of the captured first image exceeds a threshold value;adapting the first light output spectrum; and capturing a second imageof the lighting device illuminated according to the adapted first lightoutput spectrum; wherein the method further comprises: comparing thesecond image with a reference image; determining a defect in the baseplate and/or in the plurality of components based on the comparison.

According to a third aspect, the object is achieved by a controller forinspecting a lighting device during an assembly process of the lightingdevice; wherein the controller comprises: an input interface and anoutput interface; a processing unit arranged for determining a luminancecontrast measure of a first image of the lighting device illuminatedaccording to a first light output spectrum; and wherein the processingunit is further arranged for, when the luminance contrast measure of thefirst image exceeds a threshold value, adapting the first light outputspectrum, a comparing unit arranged for comparing the first or a secondimage of the lighting device illuminated according to the adapted firstlight output spectrum with a reference image; a determination unitarranged for determining a defect in a base plate and/or in a pluralityof components of the lighting device based on the comparison.

According to a fourth aspect, the object is achieved by a computerprogram product comprising instructions which, when the program isexecuted by a computer, cause the computer to carry out the steps of themethod of the second aspect.

It should be understood that the computer program product and the methodmay have similar and/or identical embodiments and advantages as theabove-mentioned systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thedisclosed systems, devices, and methods will be better understoodthrough the following illustrative and non-limiting detailed descriptionof embodiments of systems, devices, and methods, with reference to theappended drawings, in which:

FIG. 1 shows schematically and exemplary an embodiment of an inspectionsystem for inspecting a lighting device during an assembly process ofthe lighting device,

FIG. 2 shows schematically and exemplary an embodiment of a lightingdevice,

FIG. 3 shows schematically and exemplary an embodiment of a controllerfor inspecting a lighting device during an assembly process of thelighting device, and

FIG. 4 shows schematically and exemplary a flowchart illustrating anembodiment of a method for inspecting a lighting device during anassembly process of the lighting device.

All the figures are schematic, not necessarily to scale, and generallyonly show parts which are necessary in order to elucidate the invention,wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows schematically and exemplary an embodiment of an inspectionsystem 100 for inspecting a lighting device 150 during an assemblyprocess of the lighting device 150. The lighting device 150 may comprisea base plate 153 and a plurality of components 155 mounted on the baseplate 153. During the assembly process, the lighting device 150 may beelectrically unpowered, e.g. it does not receive electrical power. FIG.1 shows a side view of the lighting device 150. The base plate 153 maycomprise a metallic, a plastic or a polymer plate. A lighting device 150is a device or structure arranged to emit light suitable forilluminating an environment, providing or substantially contributing tothe illumination on a scale adequate for that purpose. A lighting device150 may comprise at least one light source or lamp, such as an LED-basedlamp, gas-discharge lamp or filament bulb, etc., optionally anyassociated support, casing or other such housing. For example, theplurality of components 155 may comprise, LED sources, LED drivers,screws, wires, labels, glue materials, paints, etc.

Each of the lighting device 150 may take any of a variety of forms, e.g.a ceiling mounted luminaire, a wall-mounted luminaire, a wall washer, ora free-standing luminaire (and the luminaires need not necessarily allbe of the same type).

The inspection system 100 may comprise a light source(s) 120 arrangedfor illuminating the lighting device 150 according to a first lightoutput spectrum for providing a luminance contrast between the baseplate 153 and the plurality of components 155. The light source 120 maya separate lighting device, external to the lighting device 150. Thelight source 120 may comprise an LED-based lamp, gas-discharge lamp orfilament bulb, etc., optionally with any associated support, casing orother such housing and may take any form. In this exemplary figure, onlyone light source 120 is shown. One or more light sources 120 may be usedin the inspection system 100. The light source 120 may be amultispectral light source arranged for illuminating the lighting deviceaccording to a first light output spectrum and a second light spectrum.Alternative to using a multispectral light source, a plurality of lightsources may be used to emit the first light output spectrum and thesecond light spectrum.

The inspection system 100 may further comprise an imaging unit 130arranged for capturing a first image of the illuminated lighting device150 illuminated according to the first light output spectrum. The firstimage is a static image of the illuminated lighting device 150. Theimaging unit 130 may be a camera. The imaging unit may be a 2D videocamera, a stereo video camera, a depth-aware (ranging) video camera(e.g. time-of-flight camera). The use of any imaging device known in theart is not excluded. In the exemplary figure, an imaging unit 130 maycomprise one imaging device. An imaging unit 130 may comprise one ormore imaging devices; wherein the first image of the illuminatedlighting device 150, for instance, may be a combination of multipleimages from the plurality of imaging devices, e.g. by performingcompositing. The imaging unit 130 may comprise a multi-spectral sensingdevice. The imaging unit 130 may comprise a thermal imaging devicearranged for capturing a first thermal image of the illuminated lightingdevice illuminated according to the first light output spectrum and/or asecond thermal image of the illuminated lighting device illuminatedaccording to the adapted first light output spectrum.

The inspection system 100 may further comprise a controller 110. Thecontroller 110 may comprise a processing unit (not shown) fordetermining a luminance contrast measure of the captured first image.The luminance contrast measure may comprise different measuresrepresenting luminance contrast of an image. One or more luminancecontrast measure(s) may be used. In an example, the luminance contrastmeasure may be pixels intensity or a variation in the pixel intensity.For example, the luminance contrast measure may be the variation inpixel intensity of the plurality of components 155 and the base plate153. The variation in pixel intensity may be for the one or morecomponents in the plurality of components. The variation may be anabrupt or expected change in intensities. In another example, theluminance contrast measure may comprise one or more of: Weber contrast,Michelson contrast, RMS contrast, contrast sensitivity function etc. TheRMS contrast is related to a change in intensities and defined as thestandard deviation of the pixel intensities. Any other measure forluminance contrast known in the art may also be used.

The processing unit may be further arranged for, when the luminancecontrast measure of the captured first image exceeds a threshold value,adapting the first light output spectrum. The processing unit may bearranged for obtaining a signal indicative of optical properties of thebase plate 153 and/or the plurality of components 155. The adaption ofthe first light output spectrum may be based on the obtained opticalproperties. The optical properties may comprise one or more of:refraction, polarization, reflection, absorption, photoluminescence(fluorescence), transmittance, diffraction, dispersion, dichroism,scattering, birefringence, color, photosensitivity etc. For example, theblue light spectrum or UV light may be used for the base plate/pluralityof components with phosphorous or fluorescent compounds. Additionally,and/or alternatively, the processing unit may be arranged for adaptingthe first light output spectrum by sequentially increasing or decreasingthe first light output spectrum. For example, by scanning differentspectrum, an optimal for the base plate 153/plurality of components 155may be achieved. The scanning of spectrums may be inputted to a computervision/machine learning algorithm(s), with the purpose to define theoptimal one or more wavelengths which may provide feature recognition.The scanning and optimizing may be referred to as an auto-calibrationthat can be repeated for each new lighting device or for each newenvironmental condition change, such as e.g. in another factory. In anexample, different spectrums may be used to determine defect indifferent one or more components of the plurality of components 155 orin the base plate 153.

The imaging unit 130 may be (then) further arranged for capturing asecond image of the lighting device 150 illuminated according to theadapted first light output spectrum. The controller 110 may control thelight source 120 to illuminate according to the adapted first lightoutput spectrum. The controller 110 may then trigger the imaging unit130 to capture the second image of the lighting device 150.

The controller 110 may further comprise a comparing unit (not shown)which may be arranged for comparing the second image with a referenceimage. The comparing unit may be arranged for using computer visionand/or machine learning algorithms for image comparison. For instance,the comparing unit may use pattern recognition algorithms, e.g.classification algorithms such as linear discriminant analysis,quadratic discriminant analysis etc., clustering algorithms such ask-mean clustering, correlation clustering etc., generative adversarialnetworks (GANs), template matching etc. The use of other computer visionand/or machine learning algorithms known in the art for detectinganomalies are not excluded. In an example, the threshold value may bedetermined by the computer vision and/or the machine learningalgorithms, e.g. to make sure that the determination of defects isperformed optimally. The controller 110 further comprises adetermination unit (not shown) arranged for determining a defect in thebase plate and/or in the plurality of components based on thecomparison. A defect may comprise one or more of absence, misplacement,misalignment, damage etc. of the base plate 153 and/or of one or more ofthe plurality of components 155. The determination unit may be furtherarranged for determining a stage of the manufacturing process bycomparing the second/first captured image with multiple reference imageseach for a different stage of the process. The comparing unit may befurther arranged for comparing the first or the second thermal imagewith a reference thermal image; and the determination unit may befurther arranged for determining a defect in the base plate 153 and/orin the plurality of components 155 based on the (thermal image)comparison.

The inspection system 100 may comprise one of more separate devicesdistributed in space, e.g. light source 120, imaging unit 130 etc.Alternatively, the inspection system 100 may be comprised in a singledevice such that the light source 120, imaging unit 130 etc. are unitsin the single device. Further, the inspection system 100 may bepartially comprised in a device, e.g. the light source 120 and theimaging unit 130 may be comprised in a single device and wherein thecontroller 110 may be comprised in a device external/separate to thelight source 120/imaging unit 130.

FIG. 2 shows schematically and exemplary an embodiment of a lightingdevice 250. The lighting device 250 may comprise a base plate 253. Thelighting device 250 may further comprise a plurality of components 255a-h, 257 a-c mounted on the base plate 253. In this exemplary figure,the plurality of components 255 a-h, 257 a-c comprises a plurality ofLED sources 255 a-h and a plurality of screws 257 a-c. The plurality ofcomponents 255 a-h, 257 a-c may further comprise wires (not shown), LEDdrivers, capacitors (not shown), resistors (not shown) etc. The interiorof a lighting device 250, and its parts (e.g. the base plate 253 and/orthe plurality of components 255 a-h, 257 a-c) that are in the opticalpathway, may be often finished in such a way that the optical efficiencyis maximized. This means often that the parts are made white in color(unless these parts would be optical components such as mirrors(specular metal) or forming optics (such as transparent lenses).

FIG. 3 shows schematically and exemplary an embodiment of a controller310 for inspecting a lighting device 150, 250 during an assembly processof the lighting device 150, 250. The controller 310 may comprise aninput interface 301. The input interface 301 may be arranged forobtaining a signal indicative of optical properties of the base plate153,253 and/or the plurality of components 155, 255 a-h, 257 a-c. Thesignal may be received from an external network such as from cloud ormay be stored in the memory 309 of the controller 310. The controller310 may further comprise an output interface 302. The output interface302 may be arranged for outputting a first control signal to the lightsource 120 related to emitting the (adapted) first light output spectrumand/or a second control signal to the imaging unit 130 related tocapturing the first and/or the second image of the lighting device 150,250. The controller 310 may further comprise a processing unit 303arranged for determining a luminance contrast measure of the capturedfirst image, wherein the processing unit 303 may be further arrangedfor, when the luminance contrast measure of the captured first imageexceeds a threshold value, adapting the first light output spectrum. Theprocessing unit 303 may be further arranged for controlling the lightsource 120 to illuminate the adapted first light output spectrum. Theprocessing unit 303 may be further arranged for controlling the imagingunit 130 to capture a second image of the lighting device 150, 250illuminated according to the adapted first light output spectrum.Additionally, and/or alternatively, the imaging unit 130 has a sensingdevice (not shown) to determine when the light output of the lightsource 120 has been changed and then capture the second image of thelighting device 150, 250.

The controller 130 may further comprise a comparing unit 305 which maybe arranged for comparing the second image with a reference image. Thecomparing unit 305 may use computer vision and/or machine learningalgorithms. The controller 130 may further comprise a determination unit307 arranged for determining a defect in the base plate 153, 253 and/orin the plurality of components 155, 255 a-h, 257 a-c, based on thecomparison.

The controller 310 may further comprise a memory 309 arranged forstoring, for instance, the first light output spectrum, the adaptedfirst light output spectrum, luminance contrast measure of the capturedfirst image, the threshold value, the computer vision and/or machinelearning algorithms, optical properties of the base plate 153,253 and/orthe plurality of components 155, 255 a-h, 257 a-c, historical data,libraries of components types, look up tables etc. The memory 309 maycomprise one or more suitable memory devices, such as one or more randomaccess memories (RAMs), read-only memories (ROMs), dynamic random accessmemories (DRAMs), fast cycle RAMs (FCRAMs), static RAM (SRAMs),field-programmable gate arrays (FPGAs), erasable programmable read-onlymemories (EPROMs), electrically erasable programmable read-only memories(EEPROMs), microcontrollers, or microprocessors.

The controller 310 may be implemented in a unit separate from the lightsource 120 and/or imaging unit 130, such as wall panel, desktop computerterminal, or even a portable terminal such as a laptop, tablet orsmartphone. Alternatively, the controller 310 may be incorporated intothe same unit as the light source 120 and/or imaging unit 130. Further,the controller 310 may be implemented remotely (e.g. on a server at adifferent geographical site); and the controller 310 may be implementedin a single unit or in the form of distributed functionality distributedamongst multiple separate units (e.g. a distributed server comprisingmultiple server units at one or more geographical sites, or adistributed control function distributed amongst the light source 120and imaging unit 130). Furthermore, the controller 310 may beimplemented in the form of software stored on a memory (comprising oneor more memory devices) and arranged for execution on a processor(comprising one or more processing units), or the controller 310 may beimplemented in the form of dedicated hardware circuitry, or configurableor reconfigurable circuitry such as a PGA or FPGA, or any combination ofthese.

Regarding the various communication involved in implementing thefunctionality, e.g. to enable the controller 310 to obtain, for instancethe optical properties of the base plate 153 and/or the plurality ofcomponents 155, 255 a-h, 157 a-c, or to control the light output of thelight source 120, these may be implemented in by any suitable wiredand/or wireless means, e.g. by means of a wired network such as anEthernet network, a DMX network or the Internet; or a wireless networksuch as a local (short range) RF network, e.g. a Wi-Fi, ZigBee orBluetooth network; or any combination of these and/or other means.

FIG. 4 shows schematically and exemplary a flowchart illustrating anembodiment of a method 400 for inspecting a lighting device 150 duringan assembly process of the lighting device 150. The method 400 maycomprise the step of illuminating 410 the lighting device 150 accordingto a first light output spectrum for providing a luminance contrastbetween the base plate 153 and the plurality of components 155, 255 a-h,257 a-c. A controller 110 may be used to control the illumination of thelight source 120. The method 400 may further comprise capturing 420 afirst image of the illuminated lighting device 150. An imaging unit 130,e.g. a camera, may be arranged for capturing the first image. The firstimage may be a static image.

The method 400 may comprise determining 430 a luminance contrast measureof the captured first image. The controller 110 may be arranged fordetermining 430 whether the luminance contrast measure of the capturedfirst image exceeds a threshold value. If the luminance contrast measureexceeds the threshold value 440 b, the method 400 may comprise adapting450 b the first light output spectrum. The controller 110 may bearranged for adapting 450 b the first light output spectrum. Adaption450 b may be performed based on the optical properties of the base plate153 and/or the plurality of components 155, 255 a-h, 257 a-c and/orbased on a scanning of different spectrums. In an example, the firstlight output spectrum is adapted for the one or more components of theplurality of components 155, 255 a-h, 257 a-c. In other words, differentspectrums may be suitable for different components. In such case,different (suitable) spectrums may be used.

The method 400 may further comprise capturing 460 b a second image ofthe lighting device 150 illuminated according the adapted first lightoutput spectrum. The second image may be captured by the imaging unit130. The method may then further comprise comparing 470 b the secondimage with a reference image. The reference image comprises an image ofthe lighting device without any defect(s). The comparing 470 b maycomprise using computer vision and/or machine learning algorithms. Themethod 400 may further comprise determining 480 b a defect in the baseplate 153 and/or in the plurality of components 155, 255 a-h, 257 a-cbased on the comparison.

When the luminance contrast measure of the captured first image does notexceed 440 a the threshold value, the method 400 may then comprisecomparing 450 a the first image with the reference image and thendetermining 460 a a defect in the base plate 153, 253 and/or in theplurality of components 155, 255 a-h, 257 a-c based on the comparison.

The method 400 may be executed by computer program code of a computerprogram product when the computer program product is run on a processingunit of a computing device, such as the processing unit 303 of thecontroller 110.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention may be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer orprocessing unit. In the device claim enumerating several means, severalof these means may be embodied by one and the same item of hardware. Themere fact that certain measures are recited in mutually differentdependent claims does not indicate that a combination of these measurescannot be used to advantage.

Aspects of the invention may be implemented in a computer programproduct, which may be a collection of computer program instructionsstored on a computer readable storage device which may be executed by acomputer. The instructions of the present invention may be in anyinterpretable or executable code mechanism, including but not limited toscripts, interpretable programs, dynamic link libraries (DLLs) or Javaclasses. The instructions can be provided as complete executableprograms, partial executable programs, as modifications to existingprograms (e.g. updates) or extensions for existing programs (e.g.plugins). Moreover, parts of the processing of the present invention maybe distributed over multiple computers or processors or even the‘cloud’.

Storage media suitable for storing computer program instructions includeall forms of nonvolatile memory, including but not limited to EPROM,EEPROM and flash memory devices, magnetic disks such as the internal andexternal hard disk drives, removable disks and CD-ROM disks. Thecomputer program product may be distributed on such a storage medium, ormay be offered for download through HTTP, FTP, email or through a serverconnected to a network such as the Internet.

1. An inspection system for inspecting a lighting device during anassembly process of the lighting device, the lighting device having abase plate and a plurality of components mounted on the base plate, theinspection system comprises: a light source arranged for illuminatingthe lighting device according to a first light output spectrum forproviding a luminance contrast between the base plate and the pluralityof components; an imaging unit arranged for capturing a first image ofthe illuminated lighting device; a controller comprising a processingunit for determining a luminance contrast measure of the captured firstimage, the processing unit further configured to adapt the first lightoutput spectrum when the luminance contrast measure of the capturedfirst image exceeds a threshold value, and the imaging unit furtherarranged for capturing a second image of the lighting device illuminatedaccording to the adapted first light output spectrum, the controllerfurther comprising a comparing unit arranged for comparing the secondimage with a reference image; and a determination unit arranged fordetermining a defect in the base plate and/or in the plurality ofcomponents based on the comparison.
 2. The inspection system accordingto claim 1; wherein the comparing unit is arranged for, when theluminance contrast measure of the captured first image does not exceedthe threshold value, comparing the first image with the reference image.3. The inspection system according to claim 1; wherein the processingunit is arranged for: obtaining a signal indicative of opticalproperties of the base plate and/or the plurality of components;adapting the first light output spectrum based on obtained opticalproperties.
 4. The inspection system according to claim 1; wherein theprocessing unit is arranged for adapting the first light output spectrumby sequentially increasing or decreasing the first light outputspectrum.
 5. The inspection system according to claim 1; wherein thelighting device is unpowered during the assembly process.
 6. Theinspection system according to claim 1; wherein the plurality ofcomponents comprises at least a phosphor coated LED.
 7. The inspectionsystem according to claim 1; wherein the comparing unit is arranged forusing computer vision and/or machine learning algorithms for imagecomparison.
 8. The inspection system according to claim 7; wherein thethreshold value is determined by the computer vision and/or the machinelearning algorithms.
 9. The inspection system according to claim 1;wherein the light source is a multispectral light source arranged forilluminating the lighting device at least according to the first lightoutput spectrum and a second light spectrum; wherein the processing unitis further arranged for, when a luminance contrast measure of an imageof the lighting device illuminated by the multispectral light sourceexceeds a threshold value; adapting the first light output spectrumand/or the second light spectrum.
 10. The inspection system according toclaim 9; wherein the imaging unit is a multi-spectral sensing device.11. The inspection system according to claim 1; wherein the imaging unitcomprises a thermal imaging device arranged for capturing a firstthermal image of the illuminated lighting device illuminated accordingto the first light output spectrum and/or a second thermal image of theilluminated lighting device illuminated according to the adapted firstlight output spectrum.
 12. The inspection system according to claim 11;wherein the comparing unit is further arranged for comparing the firstor the second thermal image with a reference thermal image; and thedetermination unit is further arranged for determining a defect in thebase plate and/or in the plurality of components based on thecomparison.
 13. A controller for inspecting a lighting device during anassembly process of the lighting device with the inspection systemaccording to claim 1; wherein the controller comprises: an inputinterface and an output interface; a processing unit arranged fordetermining a luminance contrast measure of a first image of thelighting device illuminated according to a first light output spectrum;and wherein the processing unit is further arranged for, when theluminance contrast measure of the captured first image exceeds athreshold value, adapting the first light output spectrum, a comparingunit arranged for comparing the first or a second image of the lightingdevice illuminated according to the adapted first light output spectrumwith a reference image; a determination unit arranged for determining adefect in a base plate and/or in a plurality of components of thelighting device based on the comparison.
 14. A method for inspecting alighting device during an assembly process of the lighting device withthe inspection system according to claim 1; wherein the lighting devicecomprises a base plate and a plurality of components mounted on the baseplate; wherein the method comprises the steps of: illuminating thelighting device according to a first light output spectrum for providinga luminance contrast between the base plate and the plurality ofcomponents; capturing a first image of the illuminated lighting device;determining a luminance contrast measure of the captured first image;adapting the first light output spectrum when the luminance contrastmeasure of the captured first image exceeds a threshold value; capturinga second image of the lighting device illuminated according to theadapted first light output spectrum; comparing the second image with areference image; and determining a defect in the base plate and/or inthe plurality of components based on the comparison.
 15. Anon-transitory computer-readable medium on which are stored a pluralityof non-transitory computer-readable instructions that when executed on aprocessor are configured to perform the steps comprising the method asdefined in claim 14.